Question

我的XNA项目中有一个箭头，我已成功使用此代码将其旋转到鼠标位置 -

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;

namespace Test
{
    /// <summary>
    /// This is the main type for your game
    /// </summary>
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;

        Texture2D arrowSprite;
        float rotation;
        Vector2 direction;
        Vector2 position;
        float speed;
        Vector2 mousePos;
        SpriteFont font1;

        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";
        }

        /// <summary>
        /// Allows the game to perform any initialization it needs to before starting to run.
        /// This is where it can query for any required services and load any non-graphic
        /// related content.  Calling base.Initialize will enumerate through any components
        /// and initialize them as well.
        /// </summary>
        protected override void Initialize()
        {
            // TODO: Add your initialization logic here
            position = new Vector2(GraphicsDevice.Viewport.Width / 2, GraphicsDevice.Viewport.Height / 5);
            speed = 1000.0f;
            this.IsMouseVisible = true;
            MouseState mouse = Mouse.GetState();
            mousePos.X = mouse.X;
            mousePos.Y = mouse.Y;
            rotation = Angle(position, mousePos);
            base.Initialize();
        }

        /// <summary>
        /// LoadContent will be called once per game and is the place to load
        /// all of your content.
        /// </summary>
        protected override void LoadContent()
        {
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch(GraphicsDevice);
            arrowSprite = Content.Load<Texture2D>("Sprites\\Arrow");
            font1 = Content.Load<SpriteFont>("Sprites\\Test");
            // TODO: use this.Content to load your game content here
        }

        /// <summary>
        /// UnloadContent will be called once per game and is the place to unload
        /// all content.
        /// </summary>
        protected override void UnloadContent()
        {
            // TODO: Unload any non ContentManager content here
        }

        /// <summary>
        /// Allows the game to run logic such as updating the world,
        /// checking for collisions, gathering input, and playing audio.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Update(GameTime gameTime)
        {
            // Allows the game to exit
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
                this.Exit();

            // TODO: Add your update logic here
            MouseState mouse = Mouse.GetState();
            mousePos.X = mouse.X;
            mousePos.Y = mouse.Y;
            rotation = Angle(position, mousePos);
            direction = new Vector2((float)Math.Cos(rotation), (float)Math.Sin(rotation));
            position += direction * 10.0f * (float)gameTime.ElapsedGameTime.TotalSeconds;
            base.Update(gameTime);
        }

        /// <summary>
        /// This is called when the game should draw itself.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.CornflowerBlue);

            // TODO: Add your drawing code here
            spriteBatch.Begin();
            spriteBatch.Draw(arrowSprite, position, null, Color.White, rotation, new Vector2(arrowSprite.Width / 2, arrowSprite.Height / 2), 1.0f, SpriteEffects.None, 1.0f);
            spriteBatch.DrawString(font1, mousePos.X.ToString()+ " " + mousePos.Y.ToString(), new Vector2(GraphicsDevice.Viewport.Width / 2, 0), Color.White);
            //spriteBatch.DrawString(font1, "Rotation:" + rotation.ToString(), Vector2.Zero, Color.White);
            spriteBatch.DrawString(font1, "Direction" + direction.ToString(), Vector2.Zero, Color.White);
            spriteBatch.End();
            base.Draw(gameTime);
        }

        public static float Angle(Vector2 from, Vector2 to)
        {
            return (float)Math.Atan2(from.X - to.X, to.Y - from.Y);
        }
    }
}

但是，当我运行代码时，箭头只是绕着鼠标旋转，它的半径随着时间的推移会略微扩大。我希望箭头旋转到鼠标然后它移动到它旋转到的区域。谢谢，任何帮助表示赞赏。

Answer 1

您的Angle()计算意味着箭头精灵指向其原始状态的向上。但是，您对direction的计算是错误的。计算方向和角度可以如下进行：

private void CalculateAngleAndDirection(Vector2 from, Vector2 to, out Vector2 direction, out float angle)
{
    direction = to - from; //get the direction vector
    direction.Normalize(); //make it a unit vector
    angle = (float)Math.Atan2(-direction.X, direction.Y);
}

protected override void Update(GameTime gameTime)
{
    //...
    MouseState mouse = Mouse.GetState();
    mousePos.X = mouse.X;
    mousePos.Y = mouse.Y;
    CalculateAngleAndDirection(position, mousePos, out direction, out angle); 
    position += direction * 10.0f * (float)gameTime.ElapsedGameTime.TotalSeconds;
    base.Update(gameTime);
}

Answer 2

我注意到你说了

和它的半径随着时间的推移略微扩大

并发现了这个

position += direction * 10.0f * (float)gameTime.ElapsedGameTime.TotalSeconds;

在xna中，理论上每秒调用60次，而gameTime.ElapsedGameTime.TotalSeconds每秒都会不断增加。如果要将此等式的值添加到变量位置，则由于此增量，它将逐渐改变“轨道”。此外，从我可以收集的方式来看，你正在进行旋转的方式可以返回负数（向后提供“轨道”），当乘以正浮点数时，它将返回异常数字。

XNA方向基于旋转

2 个答案: